/**
 * 2008-6-13
 */
package org.zlex.chapter09_2;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

/**
 * DSA安全编码组件
 * 
 * @author 梁栋
 * @version 1.0
 */
public abstract class DSACoder {

	/**
	 * 数字签名密钥算法
	 */
	public static final String ALGORITHM = "DSA";

	/**
	 * 数字签名
	 * 签名/验证算法
	 */
	public static final String SIGNATURE_ALGORITHM = "SHA1withDSA";
	
	/**
	 * 公钥
	 */
	private static final String PUBLIC_KEY = "DSAPublicKey";

	/**
	 * 私钥
	 */
	private static final String PRIVATE_KEY = "DSAPrivateKey";
	
	/**
	 * DSA密钥长度 
	 * 默认1024位， 
	 * 密钥长度必须是64的倍数， 
	 * 范围在512至1024位之间（含）
	 */
	private static final int KEY_SIZE = 1024;
	
	/**
	 * 签名
	 * 
	 * @param data
	 *            待签名数据
	 * @param privateKey
	 *            私钥
	 * @return byte[] 数字签名
	 * @throws Exception
	 */
	public static byte[] sign(byte[] data, byte[] privateKey) throws Exception {

		// 还原私钥
		// 转换私钥材料
		PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(privateKey);

		// 实例化密钥工厂
		KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

		// 生成私钥对象
		PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);

		// 实例化Signature
		Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);

		// 初始化Signature
		signature.initSign(priKey);

		// 更新
		signature.update(data);

		// 签名
		return signature.sign();
	}

	/**
	 * 校验
	 * 
	 * @param data
	 *            待校验数据
	 * @param publicKey
	 *            公钥
	 * @param sign
	 *            数字签名
	 * 
	 * @return boolean 校验成功返回true 失败返回false
	 * @throws Exception
	 * 
	 */
	public static boolean verify(byte[] data, byte[] publicKey, byte[] sign)
			throws Exception {

		// 还原公钥
		// 转换公钥材料
		X509EncodedKeySpec keySpec = new X509EncodedKeySpec(publicKey);

		// 实例化密钥工厂
		KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

		// 取公钥匙对象
		PublicKey pubKey = keyFactory.generatePublic(keySpec);

		// 实例话Signature
		Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);

		// 初始化Signature
		signature.initVerify(pubKey);

		// 更新
		signature.update(data);

		// 验证
		return signature.verify(sign);
	}

	/**
	 * 生成密钥
	 * 
	 * @return 密钥对象
	 * @throws Exception
	 */
	public static Map<String, Object> initKey() throws Exception {

		// 初始化密钥对儿生成器
		KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);

		// 实例化密钥对儿生成器
		keygen.initialize(KEY_SIZE, new SecureRandom());

		// 实例化密钥对儿
		KeyPair keys = keygen.genKeyPair();

		DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();

		DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();

		// 封装密钥
		Map<String, Object> map = new HashMap<String, Object>(2);

		map.put(PUBLIC_KEY, publicKey);
		map.put(PRIVATE_KEY, privateKey);

		return map;
	}

	/**
	 * 取得私钥
	 * 
	 * @param keyMap
	 *            密钥Map
	 * @return byte[] 私钥
	 * @throws Exception
	 */
	public static byte[] getPrivateKey(Map<String, Object> keyMap)
			throws Exception {

		Key key = (Key) keyMap.get(PRIVATE_KEY);

		return key.getEncoded();
	}

	/**
	 * 取得公钥
	 * 
	 * @param keyMap
	 *            密钥Map
	 * @return byte[] 公钥
	 * @throws Exception
	 */
	public static byte[] getPublicKey(Map<String, Object> keyMap)
			throws Exception {

		Key key = (Key) keyMap.get(PUBLIC_KEY);

		return key.getEncoded();
	}
}
